.box4 {
  width: 50px;
}
.layout {
  display: flex;
  justify-content: space-between;
}
.box1 {
  width: 300px;
  height: 200px;
  background-color: yellow;
  display: flex;
  justify-content: space-between;
  margin: 10px;
}
.box2 {
  margin: 20px;
  width: 100px;
  height: 100px;
  background-color: pink;
}
.box3 {
  width: 300px;
  height: 60px;
  background-color: yellow;
}
header ul {
  display: flex;
  width: 100%;
}
header ul li {
  flex-grow: 1;
}
header ul li a {
  text-decoration: none;
}
header ul li:hover {
  width: 50px;
}
